1. Field of the Invention
The invention relates to semiconductor processing equipment and, in particular, to a door for closing such equipment that, during a transfer operation, both detects objects and also maintains such objects wet.
2. Description of the Prior Art
In semiconductor manufacturing, integrated circuits are formed on silicon wafers during successive manufacturing stages involving formation and deposition of thin films on the wafers, together with selective removal of unwanted portions. To accomplish these operations, hundreds of individual steps are needed involving various pieces of process machinery, tools, measurement stations, ovens, cleaners and other equipment. Frequently, wafers are moved from one environment, such as an atmospheric pressure environment, to a different environment, such as a vacuum environment. To accomplish this, wafers are placed in cassettes or other carriers for mass transfer and the carriers are passed through a bulkhead separating the two environments. Sometimes the carriers are sealed units, such as pods known as SMIFs (Standard Mechanical Interface) or FOUPs (Front Opening Unified Pod). Other times, the cassettes are transferred outside of sealed units because the material, handling equipment does not need or use pods. For example, where a cassette is to be picked up by a robot arm, a cassette is merely transferred through a port in the bulkhead separating two environments.
In wafer handling using cassettes, it is desirable to have a wafer map indicating the number of wafers and position of the wafers within the slots of a cassette. In this patent application, the term xe2x80x9cwafer mapxe2x80x9d refers only to number and position of wafers in a cassette. Having such a wafer map, another piece of equipment, such as a robot arm could be commanded to go to specific locations in the cassette to pick up or deposit a wafer. Without a wafer map, the robot would have to rely on its own sensors to determine whether a wafer was loaded in a particular slot of a cassette. Wafer mapping units are known. For example, U.S. patent application Ser. No. 09/038,809, by J. Gordon et al., assigned to the assignee of the present invention, discloses a wafer mapper unit for use with a FOUP. In that application, a robot arm, or end effector, associated with a load port interface, carries a wafer mapper so that wafer information can be used in connection with wafer processing and manufacturing equipment.
Although use of a wafer mapper with a FOUP is a substantial benefit, a more fundamental need exists, namely to provide a wafer mapper for use with cassettes independent of a FOUP. Yet, because of the large number of measuring instruments already in a wafer manufacturing line, most manufacturers are not enthusiastic about adding another measuring station, particularly a tool which might be needed for repeated measurements as wafers advance along a manufacturing line from one stage to another.
Certain semiconductor wafer processing operations require that the surface of silicon wafers remain wet. An example of such a processing operation is chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d). Historically, silicon wafers have been kept wet by placing a cassette holding the wafers in a bath of water, usually de-ionized water. One difficulty with the preceding technique for keeping silicon wafers wet is that an operator, after turning off the, mechanical handling portion of the process, must reach a gloved hand into the water bath to retrieve the cassette.
An object of the present invention is to provide a wafer mapper tool for wafer manufacturing operations which does not require much additional space in a manufacturing line, and that can be used repeatedly between various steps in the manufacturing process.
Another object of the present invention is to provide an environment in which silicon wafers are maintained wet without immersing them within a bath of water.
Another object of the present invention is to provide an ergonomic wafer mapper tool that maintains silicon wafers wet.
Briefly, the present invention is a load port interface adapted to be secured to a bulkhead that is located between a process environment and an operator environment at a port that pierces the bulkhead. The load port interface includes a port closure assembly which when disposed in a first orientation permits an operator when present in the operator environment:
1. to deposit a cassette carrying a wafer stack, W, onto the port closure assembly; and
2. to remove a cassette carrying a wafer stack, W, from the port closure assembly.
When the load port interface is disposed in a second orientation positions the cassette carrying the wafer stack, W, in the process environment, and seals the bulkhead thereby separating the process environment from the operator environment.
The load port interface also includes means for directing droplets of liquid about a wafer stack, W, when the port closure. assembly is disposed in the second orientation. Preferably, the means for directing droplets of liquid is a plurality of nozzles which direct a spray of liquid droplets about the wafer stack, W. The preferred embodiment of the load port interface also includes a pair of spray shields that project outward from the bulkhead so the wafer stack, W, when in the operator environment, becomes disposed between both spray shields.
This load port interface also preferably includes a wafer mapper carried in the port closure assembly that has front and back panels which enclose the wafer mapper. In one embodiment, a panel acts as a box-like housing for the mapper. At the same time, at least one of the panels must seal the port through the bulkhead. To accomplish this a door of the port closure assembly is hinged in a manner allowing the door to be horizontal, on the operator side, of the bulkhead for loading and locking of a cassette onto the door, with the wafers within the cassette in a vertically upright position. A port cover plate is connected to the door panels by an angle bracket and a pivot. The cover plate has dimensions for sealing the port in the bulkhead. The cover plate makes an L-shape relative to the panel members so that each of the cover plate and the door panels is able to seal the port in the load port interface. Upon closing the door, the door moves to a vertical position by a 90 degree rotation, sealing the port, re-orienting the wafers to a horizontal position on the process side of the bulkhead. The wafers are held in place since the cassette is locked in place onto the door. The cassette is open at the top and bottom, being wider at the top than at the bottom, allowing optical inspection of the cassette through the top or bottom. Since the top of the cassette is now oriented horizontally, facing the back panel of the door, the optical inspection apparatus of the wafer mapper can determine wafer positions in the cassette through a window in the back panel of the door.
The wafer mapper consists of a miniature trolley, riding on a rail and driven by a leadscrew, all mounted between the front and rear panels of the door. The trolley carries a pair of beam sources, such as semiconductor lasers, as well as mirrors and optical detectors. The beam sources and mirrors direct a pair of beams onto the mirrors, then through a window in the trolley housing onto the expected position of a wafer. If light is reflected by a wafer edge, the optical detectors will detect the scattering, recording the reflected light signal from the wafers. The trolley is driven by a motor for advancing the trolley incrementally from one end of the door, say the upper end to the opposite end of the door and then back again. An air knife on the opposite side of the window is dragged by a magnet carried by the trolley in order to clear the window of moisture droplets. The motor is preferably a stepper motor whose motion is precisely known relative to a starting point. In this manner the known position of the trolley may be related to light scattering from individual wafers, thereby mapping the position of wafers in the cassette. The known wafer positions are recorded by a computer and passed along to other instrumentation, such as process equipment.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.